In offset lithography, a printable image is present on a printing member as a pattern of ink-accepting (oleophilic) and ink-rejecting (oleophobic) surface areas. Once applied to these areas, ink can be efficiently transferred to a recording medium in the imagewise pattern with substantial fidelity. In a wet lithographic system, the non-image areas are hydrophilic, and the necessary ink-repellency is provided by an initial application of a dampening fluid to the plate prior to inking. The dampening fluid prevents ink from adhering to the non-image areas, but does not affect the oleophilic character of the image areas. Ink applied uniformly to the wetted printing member is transferred to the recording medium only in the imagewise pattern. Typically, the printing member first makes contact with a compliant intermediate surface called a blanket cylinder which, in turn, applies the image to the paper or other recording medium. In typical sheet-fed press systems, the recording medium is pinned to an impression cylinder, which brings it into contact with the blanket cylinder.
To circumvent the cumbersome photographic development, plate-mounting, and plate-registration operations that typify traditional printing technologies, practitioners have developed electronic alternatives that store the imagewise pattern in digital form and impress the pattern directly onto the plate. Plate-imaging devices amenable to computer control include various forms of lasers.
Current laser-based lithographic systems generally rely on removal of an energy-absorbing layer from the lithographic plate to create an image. Exposure to laser radiation may, for example, cause ablation—i.e., catastrophic overheating—of the ablated layer in order to facilitate its removal. Accordingly, the laser pulse must transfer sufficient energy to the absorbing layer, leading to a trade-off between, on one hand, imaging speed and laser power, and on the other hand, layer thickness and radiation absorption. Low laser power levels and high imaging speeds are highly desirable for commercial applications. But the more these parameters are emphasized, the thinner and more absorptive the imaging layer must be. The imaging layer must also exhibit adequate adhesion to adjacent layers. Conventional imaging layers are applied at thicknesses that limit achievable increases in imaging speed and reduction of laser power requirements. Obtaining imaging layers that are thinner and more absorptive than conventional layers, while retaining adequate adhesion to adjacent layers, represents a challenging problem.